Electromagnetically operated sound producing horn



Aug. 24, 1954 R. H. BURDEN 2,687,519

ELECTROMAGNETICALLY OPERATED SOUND PRODUCING HORN Filed Oct. 10, 1950- 2Sheets-Sheet 1 Fig.1

' 5954 R. H. PURDEN 2,687,519

ELECTROMAGNETICALLY OPERATED SOUND PRODUCING HORN Filed Oct. 10, 1950 2Sheets-Sheet 2 Patented Aug. 24, 1954 ELECTROMAGNETICALLY OPERATED SOUNDPRODUCING HORN Robert Hesketh Purden,

Signor to Joseph Lucas England Solihull, England, as- Lirnited,Birmingham,

Application October 10, 1950, Serial No. 189,364

Claims priority, application Great Britain October 10, 1949 1 Claim.

This invention relates to sound producing horns, more particularly asused on road vehicles, and of the kind in which an elastic diaphragm hascombined with it an actuating electromagnet.

The object of the invention is to provide an improved constructionenabling the air gap between the stationary part of the electromagnetand its armature to be adjustable in a more convenient manner thanheretofore.

This invention comprises a construction in which the stationary part ofthe electromagnet is adjustably carried on a fixed member through themedium of screws and springs so arranged that the screws are easilyaccessible for adjustment.

In the accompanying drawings, Figure 1 is a sectional side elevation andFigure 2 a rear elevation (with cover removed) of a horn embodying theinvention.

Figure 3 is a fragmentary plan view of the electromagnet and itsarmature.

In the horn construction shown in the drawings, an air chamber a isbounded on one side by a flexible elastic diaphragm b. This chamber isin communication with a spirally formed sound-producing passage 0, ofknown kind.

According to the invention, there is secured at the rear of thediaphragm b a rigid dished metal plate at of circular form, theperiphery of the diaphragm being clamped between this plate and the parte forming the rigid side of the air chamber. In the dished plate d isformed an aperture of appropriate size and shape to accommodate thestationary part ,7 of the electromagnet on which is mounted the excitingwinding 9. The inner side of the part 1 lies in the space between thedished plate and the diaphragm, and has secured to it supporting lugs71. (Figure 3). Through plain holes in the dished plate, fixing screws2' are inserted into engagement with screw threaded holes in thesupporting lugs, and around the portion of each screw between the twoparts is mounted a stiff spring a. By rotation of the screws the extentto which the outer side of the electromagnet projects beyond the dishedplate can easily be varied (for varying the width of the air gap betweenthe electromagnet and armature k) as the outer ends of the screws areeasily accessible. The armature k is secured to a stem m which passesthrough the electromagnet and is secured to the diaphragm b. Theinterrupter n associated with the electromagnet winding is mounted inthe usual position at the outer side of the armature and is operable byan adjustable head 0 on the stem m.

To prevent inadvertent movement of the adjusting screws i abovementioned, each may be formed with a head having at one side a surfacewhich is serrated and adapted to engage corresponding serrations 10around the holes in the plate d. Alternatively any other equivalentmeans may be provided, such as a tooth on the screw head engageable witha notch on the plate.

By this invention the desired adjustability of the electromagnet air gapis provided in a very simple and convenient manner.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

An electromagnetically operable sound producing horn comprising incombination an electromagnet having a stationary part and a movablearmature situated side by side with an air gap between them, an airchamber, an elastic diaphragm bounding one side of the air chamber andoperatively connected to the armature of the electromagnet, a rigidplate secured to the air chamber, supporting lugs on the stationary partof the electromagnet, headed screws through the medium of which thestationary part Of the electromagnet is adjustable relatively to therigid plate for varying the width of the said air gap, and which extendthrough plain holes in the rigid plate towards the diaphragm and intoengagement with complementary screw threaded holes in the saidsupporting lugs, and compression springs surrounding the said screws andabutting at opposite ends respectively on the said rigid plate andsupporting lugs.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,277,587 Hill Sept. 3, 1918 1,684,906 Billig Sept. 18, 19281,696,625 Critchfield Dec. 25, 1928 2,022,367 Carbonaro Nov. 26, 19352,069,583 Lewis Feb. 2, 1937 2,120,028 Lewis Jan. 7, 1938

